Changing concepts on the control of growth hormone secretion in man.

New facts have emerged about growth hormone (hgh) secretion in man giving rise to new conceptions and to new questions.* In well-nourished, lean human beings growth hormone is released in early deep sleep and the pattern of release observed from night to night is fairly constant.* The release of growth hormone in sleep occurs when plasma glucose is not fluctuating and after insulin has fallen to a very low level. Plasma-free fatty acids may rise about two hours later but insulin does not rise in response to nocturnal hgh release.* The releases of growth hormone in sleep appear to meet the needs for a physiological test for the study of problems of growth. Correlations of this test with the many pharmacologic maneuvers in current use for diagnosis remain to be made.* Growth hormone secretion as judged by plasma concentrations relates to protein intake, such that protein depletion initiates compensatory elevation of plasma concentrations of growth hormone. Further elevations may occur with glucose loading-so-called "paradoxical" responses. In contrast, there is compensatory suppression of growth hormone secretion in obesity. Repletion of protein in the malnourished and reduction of weight in obesity cause return toward normal secretion of hgh.* Levodopa as a possible specific stimulus to growth hormone release has just been reported and the implications of this finding for the child of short stature cannot yet be assessed.